Occasionally when starting Thunderbird it takes longer than usual to start up and then when it does so the Thunderbird window has no normal decorations in the plasma desktop. Occasionally Thunderbird appears to start normally but then, when starting a compose screen or replying to email, the compose window opens, but without window decorations, and the desktop is largely frozen. All open programs appear stacked on the same screen, and all default shortcuts fail  to move to a different virtual desktop. It is not possible to click between open programs, or to access the K menu. 

Using Ctrl Alt Fx to move to a new VT is successful but returning to the graphical screen has the same symptoms as above and remains frozen.

If a spare area of the desktop is available it is possible to right click and access the "Leave" option to logout and log back in and this usually results in a normally behaving desktop again but closes all open programs in the process.

Sometimes it is possible to use the shortcut Alt-F2 to open krunner, and if so then issuing the command "kwin_x11 --replace" will repaint the screen and screen behaviour returns to normal without any loss of any running program.

Additional info:

This appears to be a kwin problem and has persisted through all versions of plasma from the initial 5 release. However this could be due to graphics rendering issues related to bugs in the qt5 packages, or mesa. The hardware on which this occurs on multiple machines for me all have Intel integrated graphics but with different graphics hardware versions. The hardware spans Ivybridge to Haswell processors with related onboard graphics.

* package version(s) 

kwin 5.5.4-1

* config and/or log files etc.

kwin support info and backtrace at the time of crash will be attached to this report.

Steps to reproduce:

Start Thunderbird and compose new mail or reply to existing mail. UI freezes.

Reproducible: Sometimes

Steps to Reproduce:
1. Login to plasma desktop
2. Start Thunderbird
3. Compose new mail or reply to existing mail.

Actual Results:  
Occasionally when starting Thunderbird it takes longer than usual to start up and then when it does the Thunderbird window has no normal decorations in the plasma desktop. Occasionally Thunderbird appears to start normally but then, when starting a compose screen or replying to email, the compose window opens but without window decorations, and the desktop is largely frozen. All open programs appear stacked on the same screen, and all default shortcuts fail  to move to a different virtual desktop. It is not possible to click between open programs, or to access the K menu. 

Using Ctrl Alt Fx to move to a new VT is successful but returning to the graphical screen has the same symptoms as above and remains frozen.

If a spare area of the desktop is available it is possible to right click and access the "Leave" option to logout and log back in and this usually results in a normally behaving desktop again but closes all open programs in the process.

Sometimes it is possible to use the shortcut Alt-F2 to open krunner, and if so then issuing the command "kwin_x11 --replace" will repaint the screen and screen behaviour returns to normal without any loss of any running program.

Expected Results:  
Thunderbird should always allow composing a new mail or reply without kwin crashing and locking up the desktop